Semiconductor devices are used in a variety of electronic applications, such as personal computers, cell phones, digital cameras and other electronic equipment. Semiconductor devices are typically fabricated by sequentially depositing insulating or dielectric layers, conductive layers, and semiconductive layers of material over a semiconductor substrate, and patterning the various layers using lithography to form circuit components and elements thereon.
Salicide technology is used to form electrical contacts between the semiconductor device and the supporting interconnect structure. The salicide process involves the reaction of a thin metal film with silicon in the active regions of the device, forming a metal silicide contact through a series of annealing and/or etch processes. Salicide formation takes place at the boundary of the front end of line (FEOL) and back end of line (BEOL). Silicide lowers the sheet resistance of the polysilicon and active silicon regions. The self-aligned silicide (salicide) relies on the principle that metal silicide will typically not form over dielectric materials, e.g., silicon nitride. Thus a metal, e.g., titanium or cobalt can be deposited over the entire surface of the wafer, and then annealed to selectively form silicide over exposed polysilicon and silicon.
The salicide process begins with deposition of a thin transition metal layer over fully formed and patterned semiconductor devices (e.g., transistors). The wafer is heated, allowing the transition metal to react with exposed silicon in the active regions of the semiconductor device (e.g., source, drain, gate), forming a low-resistance transition metal silicide. The transition metal does not react with the silicon dioxide or the silicon nitride insulators present on the wafer. Following the reaction, any remaining transition metal is removed by chemical etching, leaving silicide contacts in only the active regions of the device.
A problem in FEOL processing in dielectric materials is the formation of photoresist scum on the sidewalls and the bottom surfaces of the contact vias. The photoresist scum may cause the formation of oxides in undesired regions within the contact via, resulting in increased resistance of the contact via. Lengthy cleaning processes may be performed in an attempt to remove the photoresist scum from within the contact via. Photoresist scum increases the cost of manufacturing and may decrease product yields.
Thus, improved methods of eliminating or preventing photoresist scum are desired in semiconductor device manufacturing.